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Abstract:

An image forming method is disclosed, comprising transferring and fixing
steps, wherein fixing is performed by a fixing device in which at least
one of a heating member and a pressing member comprises an endless belt
entrained about plural rollers, and the heating member and the pressing
member are pressed against each other to form a fixing nip, and wherein
toner particles contains a binder resin which has a domain/matrix
structure constituted of a high-elastic resin forming a domain and a
low-elastic resin forming a matrix in an elastic image obtained when
observing the toner particles by an atomic force microscope with respect
to a section of the individual toner particles, in which an arithmetic
average value of a ratio (L/W) of a major axis (L) to a minor axis (W) of
individual domains is 1.5 to 5.0, and domains having the major axis (L)
of 60 to 500 nm account for not less than 80% by number of total domains
and domains having the minor axis (W) of 45 to 100 nm account for not
less than 80% by number of total domains.

Claims:

1. An image forming method comprising the steps of: (a) transferring a
toner image formed on an image support onto a transfer material, and (b)
fixing the toner image transferred onto the transfer material, wherein in
step (b), fixing is performed by a fixing device in which at least one of
a heating member and a pressing member comprises an endless belt
entrained about plural rollers, and the heating member and the pressing
member are pressed against each other to form a fixing nip, and wherein a
toner forming the toner image comprises toner particles containing a
binder resin and the binder resin has a domain/matrix structure
constituted of a high-elastic resin forming a domain and a low-elastic
resin forming a matrix in an elastic image obtained when observing the
toner particles by an atomic force microscope with respect to a section
of the individual toner particles, in which an arithmetic average value
of a ratio (L/W) of a major axis (L) to a minor axis (W) of individual
domains is in a range of 1.5 to 5.0, and domains having the major axis
(L) falling within a range of from 60 to 500 nm account for not less than
80% by number of total domains and domains having the minor axis (W)
falling within a range of from 45 to 100 nm account for not less than 80%
by number of total domains.

2. The method of claim 1, wherein the heating member comprises a rotary
roller and the pressing member comprises an endless belt entrained about
plural rollers, and a pressure-applying member which presses against the
heating member through the endless belt is provided on an inner
circumference surface of the endless belt.

3. The method of claim 1, wherein a nip length of the fixing nip is 20 to
50 mm, a surface temperature of the heating member is from 150 to
170.degree. C., a surface temperature of the pressing member is from 90
to 110.degree. C., and a difference between the surface temperature of
the heating member and the surface temperature of the pressing member
being from 40 to 70.degree. C.

4. The method of claim 1, wherein the endless belt is constituted of a
substrate formed of a heat-resistant resin, an elastic layer covering the
surface of the substrate and formed of an elastic resin, and a releasing
layer covering the elastic layer and formed of a fluororesin.

5. The method of claim 1, wherein the fixing device is provided with a
fan and a cooler constituted of a fan and a duct for introducing air
supplied by the fan in the prescribed direction.

6. The method of claim 1, wherein the toner exhibits a softening point of
90 to 110.degree. C.

7. The method of claim 1, wherein the toner exhibits a softening point of
95 to 105.degree. C.

8. The method of claim 1, wherein, in an elastic image obtained when
observing the toner particles by an atomic force microscope with respect
to a section of the individual toner particles, an arithmetic average
value of areas of individual domains is in a range of 0.01 to 0.05
μm.sup.2.

9. The method of claim 1, wherein the high-elastic resin forming a domain
exhibits a storage modulus of 4.0.times.10.sup.5 to 1.0.times.10.sup.8
dyn/cm2 at 100.degree. C.

10. The method of claim 1, wherein the low-elastic resin forming a matrix
exhibits a storage modulus of 1.0.times.10.sup.2 to 1.0.times.10.sup.4
dyn/cm2 at 100.degree. C.

Description:

[0001] This application claims priority from Japanese Patent Application
No. 2010-094725, filed on Apr. 16, 2010, which is incorporated hereinto
by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to an image forming method by use of
an electrophotographic toner.

BACKGROUND OF THE INVENTION

[0003] There have been proposed fixing devices of various systems to
heat-fixing unfixed toner images in an image forming apparatus such as an
electrophotographic copying machine, printer, or facsimile. Such fixing
devices include, for example, a fixing device of a belt-nip system in
which a fixing belt is pressed against a heating member or a pressing
member.

[0004] There is cited, for example, a fixing device of a belt-nip system,
as disclosed in JP 2004-109878A, which is constituted of a rotatably
supported heating member, an endless belt with its outer circumference
pressed against the heating member, the inner circumference of the
endless belt and a pressure-applying member, pressed against the inner
circumference of the endless belt and pressing the heating member through
the endless belt along the outer circumference of the heating member.
Such a fixing device of a belt-nip system can maintain a sufficient
nip-transit time, that is, a sufficient contact time of an unfixed toner
image with a heating member, so that an image of high gloss can be
obtained.

[0005] However, such a fixing device of a belt-nip system, in which a
pressure-applying member with an upper surface formed of an elastic layer
such as rubber is disposed with being brought into contact with the inner
circumference of an endless belt, results in increased slide resistance,
leading to unstable rotary movement and producing problems such as
occurrence of slippage of images. Specifically in cases when forming a
solid image with an increased toner adhesion amount, occurrence of
slippage of images results in microscopic wrinkles, which are visibly
observed as uneven gloss.

[0006] Accordingly, to solve such problems is disclosed a technique of
covering the upper surface of a pressure-applying member (hereinafter,
also denoted as a slide-sheet) with a sheet member of a glass fiber sheet
coated with a fluororesin (PFA) to inhibit abrasion of the inner
circumference surface of a endless belt and a technique of covering the
surface of a pressure-applying member with a slide sheet of a
concave-convex surface to lessen contact areas to reduce friction, as
described in JP 2002-148970A. However, such techniques complicate the
constitution of a fixing device, producing problems such that an exchange
cycle is shortened along with deterioration of the belts or slide sheets.

SUMMARY OF THE INVENTION

[0007] The present invention has come into being taking into account the
foregoing circumstances. It is an object of the present invention to
provide a method for forming images with enhanced gloss with inhibiting
occurrence of slippage of images.

[0008] One aspect of the present invention is directed to an image forming
method comprising the steps of:

[0009] (a) transferring a toner image formed on an image support onto a
transfer material, and

[0011] wherein in step (b), fixing is conducted by using a fixing device
in which at least one of a heating member and a pressing member comprises
an endless belt entrained about plural rollers, and the heating member
and the pressing member are pressed against each other to form a fixing
nip, and a toner forming the toner image comprises toner particles
containing a binder resin;

[0012] in an elastic image (which are hereinafter also denoted as AFM
elastic images) obtained when observing the toner particles by an atomic
force microscope (AFM) with respect to the section of the individual
toner particles, the binder resin has a domain/matrix structure
constituted of a high-elastic resin forming a domain and a low-elastic
resin forming a matrix, an arithmetic average value of a ratio (L/W) of a
major axis (L) to a minor axis (W) of the individual domains is in the
range of from 1.5 to 5.0, and domains having the major axis (L) falling
within a range of from 60 to 500 nm account for not less than 80% by
number of total domains and domains having the minor axis (W) falling
within a range of from 45 to 100 nm account for not less than 80% by
number of total domains.

[0013] To make it feasible to achieve enhanced glossiness and inhibit
slippage of images, there was studied functional separation of the
respective effects, and a toner was prepared which was composed of a
resin of low softening point and low elasticity in terms of high
glossiness and a resin of high elasticity in terms of prevention of
slippage of images. However, it was proved that sufficient effects were
not achieved by control of the structure of toner particles employing the
conventional technology. So, a toner was prepared through an orientation
manner of a resin having a domain matrix structure and enhanced
glossiness was achieved by reducing the size of the spherical domain to a
level of less than the visible light wavelength but prevention of
slippage of images was still not satisfactory.

[0014] Accordingly, the problems of the present invention were overcome by
use of a toner comprised of a binder resin having introduced a domain of
being sort of the rod shape, that is, the shape as defined in the present
invention (hereinafter, also denoted as "specific shape"). According to
the image forming method of the present invention, when using a fixing
device of a belt-nip system, the use of a specific toner inhibited
occurrence of slippage of images, while achieving glossiness of the
formed image.

[0015] The reason that occurrence of slippage of images is inhibited with
achieving glossiness of the formed image when using a fixing device of a
belt-nip system can be presumed to be as follows. Generally, in a system
of plural resins differing in thermal property being present as a
mixture, the whole of the system exhibits an averaged thermal property.
However, it is presumed that, in binder resins related to the present
invention, a high-elastic resin constituting a domain (which is
hereinafter also denoted as a domain resin) and a low-elastic resin
forming a matrix (which is hereinafter also denoted as a matrix resin)
are greatly different in thermal property, so that the matrix resin and
the domain resin exhibit no interaction with each other at a lower end of
the fixing temperature, and only the matrix resin exhibiting a low
softening point melts and the domain resin is not involved in melting, so
that the domain resin does not disturb melting deformation of a toner.

[0016] One of causes for occurrence of slippage of images is presumed to
be that, in the stage of fixing, the elasticity of a melted toner within
a fixing nip section is lowered and slide slippage is caused between the
fixing member and the transfer member, and thereby, microscopic rupture
is generated on the image surface, leaving wrinkles. It is also presumed
that, in the image forming method of the present invention, the use of a
toner in which the domain is a binder resin having a specific form
enhances the grip power of a toner forming a toner image onto a transfer
material, inhibiting occurrence of slippage of images.

[0017] Further, the reason that enhanced glossiness is achieved in the
formed image is presumed to be that the domain is a magnitude less than a
visible light wavelength and falling within a specific range, whereby the
surface of the formed image is controlled to a roughness not causing
diffused reflection.

BRIEF DESCRIPTION OF THE DRAWING

[0018] FIGS. 1a, 1b and 1c are an AMF elastic image observed by an AMF,
showing an example of the section of a toner particle related to the
present invention.

[0019]FIG. 2 illustrates a sectional view showing an example of the
constitution of the fixing device used in the image forming method of the
present invention.

[0020]FIG. 3 illustrates a sectional view showing another example of the
constitution of the fixing device used in the image forming method of the
present invention.

[0021]FIG. 4 illustrates a sectional view showing still another example
of the constitution of a fixing device used in the image forming method
of the present invention.

[0022]FIG. 5 illustrates a sectional view showing further another example
of the constitution of a fixing device used in the image forming method
of the present invention.

[0023]FIG. 6 illustrates a sectional view showing further another example
of the constitution of a fixing device used in the image forming method
of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, there will be described the present invention in
detail.

Image Forming Method:

[0025] The image forming method of the present invention comprises at
least a transfer step for transferring a toner image formed on an image
support onto a transfer material and a fixing step for fixing the toner
image transferred onto the transfer material, and specifically comprises
the following steps (1) to (5): [0026] (1) a charging step of
electrostatically charging the surface of an image support, [0027] (2) an
exposure step of exposing the electrostatically charged surface to light
to form an electrostatic latent image on the image support, [0028] (3) a
development step of developing the electrostatic latent image formed on
the image support with a developer containing a toner to form a toner
image, [0029] (4) a transfer step of transferring the toner image formed
on the image support onto a transfer material, and [0030] (5) a fixation
step of fixing the toner image transferred onto the transfer material.

[0031] In the fixing step (5), fixing is conducted by using a fixing
device in which at least one of a heating member and a pressing member
comprises an endless belt entrained about plural rollers and the heating
member and the pressing member are pressed against each other to form a
nip (which is also denoted as a fixing nip). Further, a toner which forms
the toner image comprises toner particles containing a binder resin and
in an elastic image (AFM elastic image) obtained when observing the
section of a toner particle in atomic force microscopy (AFM), the binder
resin has a domain/matrix structure comprised of a high-elastic resin
constituting a domain and a low-elastic resin constituting a matrix, an
arithmetic average value of a ratio (L/W) of a major axis (L) to a minor
axis (W) of the individual domains is in the range of from 1.5 to 5.0,
and domains having a major axis (L) falling within a range of from 60 to
500 nm account for not less than 80% by number of total domain and
domains having a minor axis (W) falling within a range of from 45 to 100
nm account for not less than 80% by number of total domains.

Toner:

[0032] The toner used in the image fanning method of the present invention
comprises toner particles containing a binder resin of a domain/matrix
structure. The toner particles related to the present invention may
optionally contain internal additives such as a colorant, a releasing
agent or a charge controlling agent.

[0033] The toner related to the invention preferably exhibits a glass
transition point of 25 to 55° C. and more preferably 30 to
45° C.

[0034] The glass transition point of a toner can be determined by using a
differential scanning calorimeter, Diamond DSC (produced by Perkin Elmer
Inc.). The measurement is conducted as follows. A toner of 4.5-5.0 mg is
precisely weighed to two places of decimals, sealed into an aluminum pan
(Kit No. 0219-0041) and set into a DSC-7 sample holder. An empty aluminum
pan is used as a reference. The temperature is controlled through
heating-cooling-heating at a temperature-rising rate of 10° C./min
and a temperature-lowering rate of 10° C./min in the range of 0 to
200° C. An extension line from the base-line prior to the initial
rise of the first endothermic peak and a tangent line exhibiting the
maximum slope between the initial rise and the peak are drawn and the
intersection of both lines is defined as the glass transition point.

[0035] The toner related to the present invention preferably exhibits a
softening point of 90 to 110° C. and more preferably 95 to
105° C. In cases when the softening point of a toner is
excessively low, it is a concern that inhibition of occurrence of
slippage of images becomes insufficient and in cases when the softening
point of a toner is excessively high, it is a concern that formed images
do not exhibit sufficiently high glossiness.

[0036] The softening point of a toner can be determined, for example, in
the manner described below.

[0037] Under an environment of 20±1° C. and 50±5% RH, 1.10 g
of a toner is placed into a petri dish, flattened, allowed to stand for
12 hrs and compressed under a pressure of 3820 kg/cm2 for 30 sec. by
using a molding machine (SSP-10A, produced by Shimazu Seisakusho Co.,
Ltd.) to form a disc-molded sample with 1 cm diameter.

[0038] Using a flow tester (CFT-500D, produced by Shimazu Seisakusho Co.,
Ltd.) and under an environment of 24±5° C. and 50+20% RH, the
thus formed sample is extruded through a hole of a cylinder type die [1
mm (diameter)×1 mm] by using a piston of 1 cm diameter after
completion of pre-heating under conditions of a load of 180N, a start
temperature of 40° C., pre-heating time of 300 sec. and a
temperature increasing rate of 6° C./min. An off-set method
temperature (Toffset) which is measured at an offset value of 5 mm
in a melting temperature measurement by a temperature increasing method,
is defined as the softening point of the toner.

[0039] Toner particles constituting the toner related to the present
invention preferably exhibit a volume-based median diameter of 3 to 12
μm, and more preferably 4 to 9 μm. Toner particles of a
volume-based median diameter falling with the foregoing range are capable
of forming an image of enhanced image quality.

[0040] The volume-based median diameter of toner particles can be
determined by using a measurement apparatus in which a Coulter Multisizer
3 (produced by Beckmann Coulter Co.) is connected to a computer system
installed with software for data processing (Software V3.51).

[0041] Toner particles constituting the toner related to the present
invention preferably exhibit an average circularity of 0.930 to 1.000,
and more preferably 0.950 to 0.995.

[0042] In the present invention, the average circularity degree can be
determined by using FPIA-2100 (produced by Sysmex Co., Ltd.).
Specifically, toner particles are blended in an aqueous surfactant
solution and dispersed using an ultrasonic homogenizer for 1 min. The
measurement condition is set to HPF (high power focusing) mode and the
measurement is carried out at an optimum concentration of the HPF
detection number of 3000-10000. Reproducible data are obtained in such a
range. The circularity degree is defined as below:

Circularity degree=(circumference length of a circle having an area
equivalent to a projection of a particle)/(circumference length of a
projection of a particle).

[0043] The average circularity degree is the sum of circularity degree
values of total particles divided by the number of particles.

Binder Resin:

[0044] A binder resin contained in toner particles constituting the toner
related to the present invention has a domain/matrix structure formed of
a high-elastic resin constituting a domain and a low-elastic resin
constituting a matrix in an AFM elastic image observed by atomic force
microscopy, that is, an elastic image obtained when observing the toner
particles by an atomic force microscope (AFM) with respect to the section
of the individual toner particles.

[0045] In the present invention, the domain structure refers to a
structure in which an area composed of a high-elastic resin exhibiting a
higher elasticity than the resin constituting the matrix, that is, a
domain is formed in a continuous matrix phase composed of a low-elastic
resin.

[0046] As is specifically shown in FIG. 1, a binder resin of the
domain/matrix structure related to the present invention is to be in a
state in which domains (denoted as light portions) composed of a domain
resin and exhibiting a specific form are dispersed in a matrix (denoted
as a dark portion) composed of a matrix resin. The domain/matrix
structure of a binder resin can be confirmed by observing the section of
a toner particle by using an atomic force microscope, SPM (SPI 3800N,
produced by Seiko Instrument Co.).

[0047] Specifically, toner particles which were subjected to humidity
conditioning under an environment of a temperature of 20° C. and a
humidity of 50% RH and hardening them, are embedded in a UV curing resin
and cured, and then sliced to clip the observation surface to prepare a
sample. Using an atomic force microscope SPM (SPI 3800N) and a cantilever
SN-AF 01 (each, made by Seiko Instrument Co.), an area of 2 μm square
was observed at room temperature, while being scanned in a
micro-viscoelastic mode. After forming pellets, they were aged with
heating to fill voids between particles, whereby measurement errors due
to surface irregularity can be prevented.

[0048] In the AFM elastic image shown in FIG. 1, there were used toner
particles containing no internal additive such as a colorant or a
releasing agent to confirm the dispersion state of a binder resin of the
domain/matrix structure. In toner particles related to the present
invention, an AFM elastic image similar to the AFM elastic image shown in
FIG. 1 is observable in an area which is not affected by an internal
additive such as a colorant or a releasing agent.

Domain:

[0049] A domain resin constituting a binder resin of a domain structure is
not specifically limited and examples thereof include a styrene-acryl
resin and a (meth)acrylic ester copolymer. A (meth)acrylic ester
copolymer is preferred in terms of its domain shape being easily
controllable, and a copolymer of methyl methacrylate, butyl acrylate and
itaconic acid is specifically preferred.

[0050] The storage modulus (that is, storage modulus of elasticity) of a
domain resin is preferably from 4.0×105 to 1.0×108
dyn/cm2 at 100° C. in terms of attainment of enhanced
glossiness a prevention of image slippage.

[0051] The storage modulus of a domain resin at 100° C. can be
determined according to a measurement instrument, conditions and the
procedure, as described below:

[0056] (1) Under an environment of 20±1° C. and 50±5% RH, 0.6
g of a domain resin is placed into a petri dish, flattened, allowed to
stand for at least 12 hrs and compressed under a pressure of 3820
kg/cm2 for 30 sec. by using a molding machine (SSP-10A, produced by
Shimazu Seisakusho Co., Ltd.) to form a disc-molded toner pellet with 1
cm diameter;

[0057] (2) The toner pellet is placed on a parallel plate installed in a
measurement instrument;

[0058] (3) After adjusting the measurement section temperature to the
softening point of the domain resin minus 50° C., a parallel plate
gap is adjusted to 3 mm;

[0059] (4) After cooling the measurement section temperature to 35°
C., the temperature of the measurement section is raised to 200°
C. at a rate of 2° C./min, while applying a sine wave oscillation
at a frequency of 1 Hz, and a storage modulus is measured at the
prescribed temperature (100° C.). The strain angle is varied
within a range of 0.02 to 5 deg. so that a torque value (R. Tolq) does
not become not more than 1%.

[0060] The storage modulus of a domain resin can be controlled by
adjusting the resin composition or molecular weight of the domain resin.
The molecular weight of a domain resin can be controlled by adjusting the
quantity of a chain-transfer agent used in the step of preparing a
dispersion of resin particles B composed of the domain resin [step (b)]
in the process of producing a toner, as described later.

[0061] In the AFM elastic image of a 2 μm square and obtained in the
manner described above, the arithmetic average value of a ratio (L/W) of
major axis (L) to minor axis (W) is preferably from 1.5 to 5.0, and more
preferably from 1.7 to 4.2.

[0062] In the AFM elastic images within the 2 μm square, obtained in
the manner described above, outlines are drawn for the individual
domains, as shown in FIG. 1a, and when sandwiching each of the outlines
between two parallel lines, the major axis (L) of the domain refers to
the maximum value of distances between the two parallel lines and the
minor axis (D) of the domain refers to the distance between two points at
which a perpendicular bisector of the major axis (L) intersects an
outline, as shown in FIG. 1b, provided that, in cases when plural
segments corresponding to W are included, the shortest distance between
the parallel two lines is defined as W. Specifically, as shown in FIG.
1c, a perpendicular bisector of the major axis (L) and the outline of the
domain intersect at four points and W1 and W2 are present, a
smaller value of W1 and W2 is defined as W.

[0063] The AFM elastic image shown in FIG. 1 indicates one in a state at
which noises arising from height signals are removed with reference to
height image falling within the same range.

[0064] In the AFM elastic image of the 2 μm square and obtained by the
method described above, domains of the major axis (L) falling within a
range of 60 to 500 nm exist in an amount of not less than 80% by number
and domains of the minor axis (W) falling within a range of 45 to 100 nm
exist in an amount of not less than 80% by number. Thus, when domains of
which the major axis (L) and the minor axis (W) satisfy the foregoing
ranges account for not less than 80% by number of total domains, the thus
formed image achieves enhanced glossiness. When domains of which the
major axis (L) and the minor axis (W) satisfy the foregoing ranges
account for less than 80% by number of total domains, the formed image
does not attain sufficiently high glossiness and does not attain
sufficient resistance to image slippage. Specifically, in cases when the
major axes (L) of the domains exceed 500 nm or the minor axes (W) exceed
100 nm, the thus formed image does not achieve sufficiently high
glossiness and does not attain sufficient resistance to image slippage.
On the other hand, in cases when the major axes (L) of the domains is
less than 100 nm or the minor axes (W) is less than 45 nm, sufficient
resistance to image slippage cannot be attained.

[0065] The minor axis (W) of a domain can be controlled by adjusting the
particle size of resin B particles composed of a domain resin in the
method of producing a toner [specifically, at step (b)], as described
later. The particle size of the resin B particles can be controlled in
the process of producing the resin B particles, preferably by adjusting
the amount of a surfactant added in the process of emulsion
polymerization. The major axis (L) of a domain can be controlled by
adjusting the ratio (MID) of addition mass (M) of resin A particles
composed of a matrix resin to addition mass (D) of resin B particles
composed of a domain resin in the method of producing a toner
[specifically, at step (d)], as described later. Specifically, it is
preferred to control the ratio (MID) so as to fall within the range, as
defined in the following formula (1):

70/30≦M/D≦95/5 Formula (1)

[0066] In the AFM elastic image of a 2 μm square, obtained by the
method described above, the arithmetic average value of areas of the
individual domains is preferably in the range of from 0.005 to 0.05
μm2, and more preferably from 0.01 to 0.05 μm2. When the
arithmetic average value of areas of the individual domains falls within
the foregoing range, domains of moderate size are dispersed in the
matrix, whereby image slippage is inhibited, while achieving enhanced
glossiness of the formed image. When the arithmetic average value of
areas of the individual domains is less than 0.005 μm2, it is a
concern that sufficient resistance to image slippage is not attained. On
the other hand, when the arithmetic average value of areas of the
individual domains exceeds 0.05 μm2, it is a concern that an
image of enhanced glossiness is not formed with enhanced reproducibility.

[0067] The area (S) of a domain is calculated by the following equation
(1):

S(μm2)=(L×W){W2-π(1/2W)2} Equation (1)

[0068] The glass transition point of a domain resin is preferably from 60
to 80° C., and more preferably from 63 to 68° C. in terms
of controlling the major axis (L) and minor axis (W) of a domain.

[0069] The glass transition point of a domain resin can be determined by
using a differential scanning calorimeter, Diamond DSC (produced by
Perkin Elmer Inc.). The measurement is conducted as follows. A domain
resin (domain resin particles) of 4.5-5.0 mg is precisely weighed to two
places of decimals, sealed into an aluminum pan (Kit No. 0219-0041) and
set into a DSC-7 sample holder. An empty aluminum pan is used as a
reference. The temperature is controlled through heating-cooling-heating
at a temperature-rising rate of 10° C./min and a
temperature-lowering rate of 10° C./min in the range of 0 to
200° C. An extension line from the base-line prior to the initial
rise of the first endothermic peak and a tangent line exhibiting the
maximum slope between the initial rise and the peak are drawn and the
intersection of both lines is defined as the glass transition point.

[0070] The softening point of a domain resin is preferably from 150 to
200° C., and more preferably from 170 to 190° C. When the
softening point of a domain resin falls within the foregoing range,
sufficient resistance to hot offset can be achieved.

[0071] The softening point of a domain resin can be determined, for
example, in the manner described below.

[0072] Under an environment of 20±1° C. and 50±5% RH, 1.10 g
of a domain resin is placed into a petri dish, flattened, allowed to
stand for 12 hrs and compressed under a pressure of 3820 kg/cm2 for
30 sec. by using a molding machine (SSP-10A, produced by Shimazu
Seisakusho Co., Ltd.) to form a disc-molded sample with 1 cm diameter.

[0073] Using a flow tester (CFT-500D, produced by Shimazu Seisakusho Co.,
Ltd.) and under an environment of 24±5° C. and 50±20% RH,
the thus formed sample is extruded through a hole of a cylinder type die
(1 mm×1 mm) by using a piston of 1 cm diameter after completion of
pre-heating under conditions of a load of 196 N (20 kgf), a start
temperature of 60° C., pre-heating time of 300 sec. and a
temperature increasing rate of 6° C./min. The off-set method
temperature (Toffset) which is measured at an offset value of 5 mm
in a melting temperature measurement by a temperature increasing method,
is defined as the softening point of the domain resin.

[0074] The mass average molecular weight (Mw) of a domain resin, which is
represented by equivalent converted to standard polystyrene, is
preferably from 10,000 to 350,000, and more preferably from 250,000 to
300,000.

[0075] The mass average molecular weight (Mw) can be determined by gel
permeation chromatography (GPC) and is performed in the following manner.
Using an apparatus, HLC-8220 (produced by TOSO Co., Ltd.) and a column,
TSK guard column+TSK gel Super HZM-M3 3 Series (produced by TOSO Co.,
Ltd.), tetrahydrofiran (THF) as a carrier solvent is allowed to flow at a
flow rate of 0.2 ml/min, while maintaining a column temperature at
40° C. The domain resin is dissolved in tetrahydrofuran (THF) at
room temperature, while being stirred over 5 min. by an ultrasonic
homogenizer to obtain a solution at a concentration of 1 mg/ml.
Subsequently, the solution is filtered with a membrane filter having a
pore size of 0.2 μm to obtain a sample solution. Into an apparatus was
injected 10 μl of the obtained sample solution together with the
foregoing carrier solvent and detected by using a refractive index
detector (RI detector). The molecular weight distribution of a sample is
determined by use of a calibration curve which was prepared by using
monodisperse polystyrene standard particles to determine the molecular
weight. There were used 10 points of standard polystyrene samples used
for preparation of a calibration curve.

[0076] The content of a domain resin is preferably from 2.5 to 30% by mass
of the whole of a binder resin, and more preferably from 2.5 to 15% by
mass. When the content of the domain resin falls within the foregoing
range, image slippage is inhibited, while achieving enhanced glossiness
of the formed image.

Matrix:

[0077] A matrix resin constituting a binder resin of the domain/matrix
structure is not specifically limited but is appropriately chosen
according to the main performance required as a toner (for example,
glossiness, fixability, etc.), and examples thereof include a polyester
resin and a styrene-acryl resin.

[0078] The storage modulus of elasticity of a matrix resin at 100°
C. is preferably from 1.0×102 to 1.0×104
dyn/cm2. When the storage modulus of a matrix resin at 100°
C. is less than 1.0×102 dyn/cm2, it is a concern that
sufficient resistance to image slippage is not achieved. On the other
hand, when the storage modulus of a matrix resin at 100° C.
exceeds 1.0×104 dyn/cm2, it is a concern that an image of
high glossiness can not be formed with enhanced reproducibility.

[0079] The glass transition point of a matrix resin is preferably from 25
to 50° C. in terms of achieving low temperature fixability, and
more preferably from 30 to 40° C.

[0080] The softening point of a matrix resin is preferably from 80 to
120° C. in terms of achieving enhanced glossiness, and more
preferably from 90 to 100° C.

[0081] The mass average molecular weight of a matrix resin is preferably
from 10,000 to 30,000, and more preferably from 15,000 to 25,000.

[0082] Measurement methods for storage modulus, glass transition point,
softening point and mass average molecular weight (Mw) of a matrix resin
are respectively the same as for the above-described methods for storage
modulus, glass transition point, softening point and mass average
molecular weight (Mw) of a matrix resin, except that the domain resin is
replaced by a matrix resin (or resin particles composed of a matrix
resin).

[0083] In the toner related to the present invention, a binder resin is
comprised of a high-elastic resin constituting a domain and a low-elastic
resin constituting a matrix, and there may be contained at least a
commonly known resin other than the high-elastic resin and the
low-elastic resin.

Colorant:

[0084] Colorants used for toner particles constituting the toner related
to the present invention can employ commonly known dyes and pigments.
Colorants to obtain a black toner can employ those known to one skilled
in the art, such as carbon black, a magnetic material, a dye, and an
inorganic pigment containing a non-magnetic iron. Colorants to obtain a
color toner can employ commonly known dyes and organic pigment. Colorants
to obtain the individual color may employ one or more of them.

[0085] The content of a colorant is preferably from 1 to 10% by mass, and
more preferably from 2 to 8% by mass. When the colorant content is less
than 1% by mass, it is a concern that a toner is insufficient in coloring
power; and when a colorant content exceeds 10% by mass, it is a concern
that colorant release or its adhesion to a carrier or the like occurs,
adversely affecting electrostatic-charging property.

Releasing Agent:

[0086] Releasing agents used for the toner related to the present
invention are not specifically restricted and examples thereof include
polyethylene wax, oxidized polyethylene wax, polypropylene was, oxidized
polypropylene wax, carnauba wax, sasol wax, rice wax, and candelilla wax.
The amount of wax contained in toner particles is preferably from 0.5 to
25 parts by mass of 100 parts by mass of a binder resin, and more
preferably from 3 to 15 parts by mass.

Charge Control Agent:

[0087] A charge control agent used for toner particles constituting the
toner related to the present invention can employ commonly known
compounds such as a metal complex, an ammonium salt, and calixarene. The
amount of a charge control agent contained in toner particles is
preferably from 0.1 to 10 parts by mass of 100 parts by mass of a binder
resin, and more preferably from 0.5 to 5 parts by mass.

External Additive:

[0088] Toner particles constituting the toner related to the present
invention may be used as a toner without any change, but so-called
external additives such as a fluidizing agent or a cleaning aid to
improve fluidity, electrostatic-charging property or cleaning capability.
Examples of such a fluidizing agent include inorganic particles composed
of silica, alumina, titanium oxide, zinc oxide, iron oxide, copper oxide,
lead oxide, antimony oxide, yttrium oxide, magnesium oxide, barium
titanate, ferrite, colcothar, magnesium fluoride, silicon carbide, boron
carbide, silicon nitride, zirconium nitride, magnetite or magnesium
stearate. It is preferred that these inorganic particles are subjected to
a surface treatment by use of a silane coupling agent, a titanium
coupling agent, a higher fatty acid or silicone oil to achieve enhanced
dispersibility or environmental stability.

[0089] Examples of a cleaning aid include polystyrene particles and
poly(methyl methacrylate) particles.

[0090] External additives may be used singly or in combination of them. A
total addition amount of external additives is preferably from 0.1 to 20%
by mass of a toner.

Developer:

[0091] The toner related to the present invention may be used as a
magnetic or non-magnetic single-component developer or mixed with a
carrier to be used as a two-component developer. In cases when using the
toner of the present invention as a two-component developer, there are
usable magnetic particles composed of commonly known materials, for
example, a metal such as iron, ferrite or magnetite, or an alloy of such
a metal and a metal such as aluminum or lead. Of these materials are
preferred ferrite particles. A carrier may employ a coated carrier in
which the surface of a magnetic particle is coated with a covering agent
such as a resin or a dispersion type carrier formed of a powdery magnetic
material dispersed in a binder resin.

[0092] The volume-based median diameter of a carrier is preferably from 15
to 100 μm, and more preferably from 20 to 80 nm. The volume-based
median diameter of a carrier can be measured by laser diffraction sensor
HELOS (produced by SYMPATECS Co., Ltd.) which is installed with a wet
disperser.

[0093] Examples of a preferred carrier include a resin coverage carrier in
which the surfaces of magnetic particles are covered with a resin and a
resin dispersion type carrier in which magnetic particles are dispersed
in a resin. Resins constituting such a resin coverage carrier are not
specifically limited and examples thereof include an olefinic resin, a
styrene resin, a styrene-acryl resin, a silicone resin, an ester resin
and a fluorine-containing polymer resin. A resin constituting a resin
dispersion type carrier is not specifically limited but can employ resins
commonly known in the art, and examples thereof include a styrene-acryl
resin, a polyester resin, a fluorinated resin and a phenol resin.

Production Method of Toner:

[0094] A method for producing a toner related to the present invention is
not specifically limited so long as it is a method capable of obtaining
toner particles containing a binder resin in which domains formed of a
domain resin and having a specific form are dispersed in a matrix formed
of a matrix resin, of which an emulsion polymerization aggregation method
or a mini-emulsion polymerization aggregation method is preferred, in
which a domain resin can be easily introduced into a matrix resin.

[0095] As a method for producing a toner related to the present invention
is shown below specific steps (a)-(h) of an emulsion polymerization
aggregation method. The method comprises the steps of:

[0096] (a) the step of preparing a dispersion (A) of resin A particles
comprised of a low-elastic resin constituting a matrix,

[0097] (b) the step of preparing a dispersion (B) of resin B particles
comprised of a high-elastic resin constituting a domain and exhibiting a
glass transition temperature of 60 to 80° C. and a softening point
of 150 to 200° C.;

[0098] (c) the step of preparing a dispersion (X) of fine particles of a
colorant (hereinafter, also denoted as colorant particles);

[0099] (d) the step of mixing a dispersion (A), a dispersion (B) and a
dispersion (X) and allowing the resin A particles, the resin B particles
and the colorant particles to coagulate and fuse to form aggregated
particles;

[0100] (e) the step of adding particles used for shelling to form a shell
layer;

[0101] (f) the step of ripening the particles to control a domain-matrix
structure, while stirring under the temperature condition near the
softening point of the resin A particles and less than the softening
point of the resin B particles;

[0102] (g) the step of filtering off the aggregated particles from a
coagulated particle dispersion (with an aqueous medium) to remove a
surfactant and the like from the aggregated particles; and

[0103] (h) the step of drying the thus washed particles to obtain toner
particles; and the shelling step (e) may optionally be conducted.

[0104] In the present invention the aqueous medium refers to a medium
composed of 50 to 100% by mass of water and 0 to 50% by mass of an
aqueous soluble organic solvent. Examples of such a aqueous-soluble
organic solvent include methanol, ethanol, isopropanol, butanol, acetone,
methyl ethyl ketone, and tetrahydrofuran. Of these is preferred an
alcoholic organic solvent which does not dissolve the obtained resin.

Step (a):

[0105] The resin A particles can be prepared through an emulsion
polymerization method, a seed polymerization method or a mini-emulsion
polymerization method by using a radical-polymerizable monomer as a raw
material. They can also be prepared through a phase inversion method in
which a resin solution of an organic solvent is subjected to phase
inversion in an aqueous medium.

[0106] The resin A particles may be constituted of at least two layers
formed of resins differing in composition, which can be prepared in such
a manner that, to a dispersion of resin particles prepared according to
the conventional emulsion polymerization process (1st polymerization), a
polymerization initiator and a polymerizable monomer are added and
subjected to a polymerization treatment (2nd polymerization).

[0107] The resin A particles preferably exhibit a volume-based median
diameter falling within a range of from 45 to 350 nm, and more
preferably, from 45 to 210 nm. The volume-based median diameter of the
resin A particles can be determined in the manner in which a few drops of
a sample are added into a measuring cylinder, pure water is added thereto
and a mixture is dispersed in an ultrasonic washing machine (US-1,
produced by AS ONE Corp.) to prepare a measuring sample, and the thus
prepared sample is measured by using Micro Track UPA-150 (produced by
Nikkiso Co., Ltd.).

[0108] The resin A particles preferably exhibit a glass transition point
of from 25 to 50° C., and more preferably, from 90 to 100°
C.

[0109] A polymerization initiator used in the step (a) can employ any
water-soluble polymerization initiator. Examples of such a polymerization
initiator include a persulfate (e.g., potassium persulfate, ammonium
sulfate), an azo compound [e.g., 4,4'-azobis-4-cyanovalerianic acid and
its salt, 2,2'-azobis(2-amidinopropane) salt] and a peroxy-compound.

Chain Transfer Agent:

[0110] In the step (a) are usable conventionally used chain transfer
agents to control the molecular weight of the resin A particles. A chain
transfer agent is not specifically limited and examples thereof include
2-chloroethanol, mercaptans such as octylmercaptan, dedecylmercaptan,
t-decymercaptan, and styrene dimmer.

Surfactant:

[0111] In the step (a), there may be added a surfactant to allow the resin
particles to be stably dispersed. Such a surfactant is not specifically
restricted and various surfactants are usable, but preferred examples of
an ionic surfactant include a sulfonate such as sodium
dodecybenzenesulfonate or sodium arylalkyl-polyether-sulfonate; a
sulfuric acid ester salt such as sodium dodecysulfate, sodium
tetradecylsulfate, sodium pentadecylsulfate, or sodium octylsulfate; and
a carboxylic acid salt such as sodium oleate, sodium laurate, sodium
caprate, sodium caprylate, sodium caproate, potassium stearate, and
calcium oleate. There are also usable nonionic surfactants such as
polyethylene oxide, polypropylene oxide, a combination of polyethylene
oxide and polypropylene oxide, an ester of polyethylene glycol and a
higher fatty acid, alkylphenol polyethyleneoxide, an ester of a higher
fatty acid and polyethylene glycol, an ester of a fatty acid and
polypropylene oxide, and sorbitan ester. Such surfactants may be used
singly or in combination of them.

Step (b):

[0112] The resin B particles can be prepared by the process of emulsion
polymerization, seed polymerization or mini-emulsion polymerization, with
using a radical-polymerizable monomer. It can also prepared by a process
of phase inversion emulsification, in which a resin solution using an
organic solvent is subjected to phase inversion in an aqueous medium.

[0113] With respect to the particle size of the resin B particles, the
volume-based median diameter thereof falls preferably within the range of
from 30 to 140 nm, and more preferably from 45 to 100 nm.

[0114] The volume-based median diameter of the resin B particles can be
determined in the same manner as in the resin A particles described
above, except that a measurement sample is replaced by the resin B
particles.

[0115] The glass transition point of the resin B particles is preferably
from 60 to 80° C., and more preferably from 63 to 68° C.;
the softening point of the resin B particles is preferably from 150 to
200° C., and more preferably from 170 to 190° C.

[0116] In the step (b) are usable a polymerization initiator, a chain
transfer agent and a surfactant which are similar to those used in the
step (a).

Step (c):

[0117] The particle size of colorant particles falls preferably within the
range of 10 to 300 nm in terms of volume-based median diameter.

[0118] The volume-based median diameter of the colorant particles can be
determined in the same manner as in the resin A particles described
above, except that the measurement sample is replaced by the colorant
particles.

Step (d):

[0119] In the step (d), the coagulation temperature preferably is higher
than the glass transition point of the resin A particles, whereby the
resin A particles are fused, while being coagulated, and are fused with
the resin B particles and the colorant particles to obtain aggregated (or
coalesced) particles.

[0120] In the step (d), the major axis of a domain can be controlled by
adjusting an addition ratio of resin A particles to resin B particles.
Specifically, it is preferred to control the ratio (M/D) of addition mass
(M) of the resin A particles to mass (D) of the resin B particles so as
to fall within the range defined in the following relational expression
(1):

70/30≦M/D≦95/5 Expression (1):

[0121] In the step (d), the temperature is raised, while adding a
coagulant, whereby coagulation is initiated.

Coagulant:

[0122] Coagulants usable in the step (d) include, for example, an alkali
metal salt and an alkaline earth metal salt. Alkali metals capable of
forming a coagulant include lithium, potassium and sodium; alkaline earth
metals capable of forming a coagulant include magnesium, calcium,
strontium and barium. Of these are preferred potassium, sodium,
magnesium, calcium and barium. Counter ions of the foregoing alkali metal
or alkaline earth metal (that is, anions constituting a salt) include a
chloride ion, a bromide ion, an iodide ion, a carbonate ion and a sulfate
ion.

Step (e):

[0123] In the method of preparing the toner related to the present
invention, the resin A particles and the resin B particles are subjected
to coagulation and fusion to form a binder resin of a domain/matrix
structure. It is preferred to form a core portion with the resin of a
domain/matrix structure and to form a shell with a resin (hereinafter,
also denoted as a shelling resin) differing in composition from the
domain resin and the matrix resin.

Step (f):

[0124] In the step (f), aggregated particles are ripened under the
temperature condition near the softening point of the resin A particles
but less than the softening point of the resin B particles. Under such
temperature conditions, the step of ripening aggregated particles,
whereby the major axis of the domain is controlled. The temperature near
the softening point of the resin A particles is preferably within the
range of (softening point of the resin A)±10° C.

[0125] It is presumed that, in the step (f), after the resin A particles
and the resin B particles are coagulated and fused, orientation of the
resin B which has not completely been melted, proceeds slowly in a matrix
resin derived from the resin A particles of relatively lowered viscosity.
Further, it is presumed that the domain forms a specific form
specifically in the ripening step of ripening coagulated particles under
the temperature condition of being higher than the glass transition point
and lower than the softening point of the resin B. It is presumed that,
in the step (f), single or plural resin B particles (specifically, 2-4
particles) are coagulated on a single axis to form a domain of a specific
form.

[0126] The ripening step is conducted, while stirring at a temperature
falling within the range, as follows. Namely, the ripening temperature is
preferably 60 to 97° C., and more preferably, 70 to 90° C.,
and the ripening time is preferably 1 to 6 hours in terms of controlling
a specific form of the domain.

Steps (g) to (h):

[0127] These steps can be conducted in accordance with ones generally
known and employed.

[0128] In cases when internal additives are contained in the toner
particles related to the present invention, for example, a dispersion of
internal additive particles composed of an internal additive alone is
prepared prior to the step (d), and in the step (d), the dispersion of
internal additive particles is mixed with the respective dispersions and
the internal additive particles are coagulated together with resin A
particles, resin B particles and colorant particles, whereby the internal
additive can be introduced into the interior of toner particles.

Fixing Device:

[0129] In the fixing step of the image forming method of the present
invention, fixing is conducted by a fixing device in which at least one
of a heating member and a pressing member comprises an endless belt
entrained about plural rollers and the heating member and the pressing
member are pressed against each other to form a fixing nip. Hereinafter,
there will be described embodiments of a fixing device used in the image
forming method of the present invention.

[0130]FIG. 2 illustrates a sectional view showing an example of the
constitution of the fixing device used in the image forming method.

[0131] A fixing device 10, which employs a belt nip system, is provided
with a heating member 11 formed of a rotating roller (which is
hereinafter also denoted as a heating roller 11), an endless belt 12A
entrained about three rollers and a pressing member 12 formed of a
pressure-applying member 12B, in which a fixing nip section N is formed
by a pressing portion between the heating roller 11 and the
pressure-applying member 12B in the pressing member 12.

[0132] A nip length of the fixing nip section N is preferably from 20 to
50 mm. When the nip length of the fixing nip section N falls within the
foregoing range, image slippage is inhibited, while the formed image
achieves enhanced glossiness. In the fixing device 10, the nip length of
the fixing nip section N is, for example, 35 mm.

[0133] The heating roller 11 is built-in with a heating source 13
comprised of a halogen heater and the heating source 13 is constituted of
an internally disposed, metallic cylindrical core 11a and a
heat-resistant elastic material layer 11b formed on the circumference
surface of the cylindrical core bar 11a.

[0134] The cylindrical core bar 11a constituting the heating roller 11 is
constituted of a metal exhibiting a high heat conductivity, for example,
iron, aluminum or an alloy. The heat-resistant elastic material layer 11b
constituting the heating roller 11 is constituted of, for example, an
elastic layer formed of a highly heat-resistant HTV silicone rubber and a
releasing layer covering the elastic layer and formed of a fluororesin
such as perfluoroalkyl vinyl ether (PFA) or polytetrafluoroethylene
(PTFE).

[0135] The surface temperature (T1) of the heating roller is
preferably 130 to 170° C. (more preferably, 150 to 170° C.)
in cases of a fixing linear speed of 340 mm/sec. A heating member
temperature detector 101a is opposingly disposed on the surface of the
heating roller 11 and based on a temperature measurement value of the
temperature detector 101a, the heating source 13 is controlled by the
control section of the image forming apparatus (not shown in the
drawing), whereby the surface temperature (T1) of the heating roller
11 is set. When the surface temperature (T1) of the heating roller
11 is excessively low, it is a concern that the formed image cannot
achieve high glossiness; on the other hand, when the surface temperature
(T1) of the heating roller 11 is excessively high, it is a concern
that occurrence of image slippage is not sufficiently inhibited.

[0136] The pressing member 12 is constituted of the endless belt 12A
entrained about belt-entraining rollers 12a, 12b and a pressure roller
12c, and the pressure-applying member 12B which presses the heating
roller 11 onto the inner circumference of the endless belt 12A through
the endless belt 12A.

[0137] The endless belt 12A constituting the pressing member 12A is
entrained about the outer circumference of each of the belt-entraining
roller 12a which is provided upstream from the fixing nip section N in
the conveyance direction of a transfer material P, the belt-entraining
roller 12n supporting the endless belt 12A and the pressure roller 12c
which is provided downstream from the fixing nip section N, is in an
endless form which is rotatably supported, and is rotatably driven with
rotation of the belt-entraining rollers 12a and 12b and the pressure
roller 12c.

[0138] The endless belt is constituted of a substrate formed of
heat-resistant resin such as a polyimide, an elastic layer covering the
surface of the substrate and formed of an elastic resin such as a
silicone rubber, and a releasing layer covering the elastic layer and
formed of a fluororesin such as PFA or PTFE.

[0139] The pressure-applying member 12B constituting the pressing member
12 is constituted of the pressure roller 12c and a pressure-applying
member 12e. The pressure-applying member 12B is disposed while being in
contact with the inner circumference of the endless belt 12A. The
pressure-applying member 12B presses the heating roller 11 through the
endless belt 12A from the inner circumference side of the endless belt
12A, whereby the fixing nip section N is formed between the heating
roller 11 and the endless belt 12A.

[0140] The pressure roller 12c constituting the pressure-applying member
12B is provided in an are downstream from the fixing nip section N in the
conveyance direction of the transfer material P. The pressure roller 12c
exhibits a higher hardness than first, second and third pads 121, 122 and
123, and constituted of a cylindrical core bar formed of a metal such as
aluminum, iron or an alloy. The pressure roller 12c has a function of
supporting the endless belt 12A, while pressing the heating roller 11
from the inner circumference side of the endless belt 12A.

[0141] The pressing member 12e constituting the pressure-applying member
12B is constituted of a compression spring applying pressing power (not
shown in the drawing), a holder housing these (not shown in the drawing)
and a sliding sheet (not shown in the drawing) which is in contact with
the inner circumference of the endless belt 12A covering the upper
surfaces of the first pad 121 and the third pad 123, while supporting the
first pad 121, the second pad 122, the third pad 123 and a supporting
member 124.

[0142] The first pad 121 and the second pad 122 constituting the pressing
member 12e form a member layer which is layered in a direction
perpendicular to the conveyance direction of the transfer material P, and
are provided in an are upstream from the fixing nip section N in the
conveyance direction of the transfer material P. The first pad 121 which
is a layer (upper layer) nearest to the fixing nip section N exhibits a
lower hardness than the second pad 122 which is a layer (lower layer)
farthest from the fixing nip section N.

[0143] The hardness of the whole member layers constituting the pressing
member 12e is higher than that of the first pad 121 and not more than
that of the second pad 122. For example, the first pad 121 is formed of a
heat-resistant sponge and the second pad is formed of a heat-resistant
urethane, whereby the hardness of the whole member layers becomes higher
than that of the first pad 121 and lower than that of the second pad 122.

[0144] The third pad 123 constituting the pressing member 12e is disposed
in a central region of the fixing nip section N along the conveyance
direction of the transfer material P, that is, between a member layer
constituted of the first pad 121 and the second pad 122 and the pressure
roller 12c. The third pad 123 exhibits a lower hardness than the whole
member layer constituted of the first pad 121 and the second pad 122. The
third pad 123 is constituted of an elastic material, such as a heat
resistant silicone rubber.

[0145] The supporting member 124 constituting the pressing member 12e is
constituted of a metal plate such as stainless steel, supporting the
first, second, third pads 121, 122, 123, and a resin plate supporting the
metal plate, and is formed of a rigid material capable of maintaining a
strength of not being broken even when subjected to an elastic force of a
compression spring. The elastic force of the compression spring is
provided as a constant compression power against the endless belt 12A
through the supporting member 124, and the first, second, third pads 121,
122 and 123.

[0146] Herein, there will be described distribution of compression force
within a fixing nip section in the conveyance direction of the transport
material P. As described above, the pressure-applying member 12B is
constituted of a member layer comprised of the first pad and the second
pad 122 which are provided in the area upstream from the fixing nip
section N along the conveyance direction of the transfer material P, the
third pad 123 provided in the central region, and a pressure roller 12c
provided in an area downstream, each of which exhibits a different
hardness. The hardness (H1) of the whole member layer constituted of the
first pad 121 and the second pad 122, the hardness (H2) of the third pad
123 and the hardness (H3) of the pressure roller 12c satisfy the
following expression 1:

H3>H1>H2. Expression 1

[0147] The upstream area from the fixing nip section N in the conveyance
direction of the transfer material P is subject to a pressure power P1
from a member layer constituted of the first pad 121 and the second pad
122. The downstream area from the fixing nip section N in the conveyance
direction of the transfer material P is subject to a compression power P3
from the compression roller 12c. The central region of the fixing nip
section N in the conveyance direction of the transfer material P is
subject to a compression power P2 from the third pad 123. Accordingly,
the distribution of compression power within the fixing nip section N is
represented by the following expression 2:

P3>P1>P2 Expression 2

[0148] The surface temperature (T2) of the pressing member 12,
specifically, the endless belt 12A, is preferably from 90 to 110°
C. in cases when the fixing linear rate is 340 mm/sec. A temperature
detector 101b for the pressing member is opposedly disposed on the
surface of the endless belt and the surface temperature (T2) of the
endless belt 12A is detected by the temperature detector 101b. The
difference (T1-T2) between the surface temperature (T1) of
the heating roller 11 and the surface temperature (T2) of the
pressing member 12 is preferably from 40 to 70° C. In cases when
the difference (T1-T2) falls within the foregoing range, an
image of enhanced glossiness can be formed. When the difference
(T1-T2) is excessively small, an image of enhanced glossiness
may be formed but resistance to image slippage is lowered, producing a
concern that uniformity of image glossiness becomes totally unstable.

[0149] In the fixing device 10, when the endless belt is rotated in the
direction indicated by the arrow with being connected to a driving motor
(not shown in the drawing), in accordance with this rotation, the endless
belt 12A is moved in the same direction at the fixing nip section N of
being pressed against the heating roller 11, and when the transfer
material P, onto which a toner image is transferred, passes through the
fixing nip section N, the toner image on the transfer material P is fixed
by pressure from the pressure-applying member 12B and applied onto the
fixing nip section N.

[0150] Thus, the fixing device which is suitably used for the image
forming method of the present invention is described with respect to its
embodiments, however, a fixing device used in the image forming method of
the present invention is not limited to the foregoing embodiments and
various variations can be employed. Hereinafter, there will be
specifically described other embodiments.

[0151]FIG. 3 illustrates a sectional view showing another example of the
constitution of the fixing device used in the image forming method. A
fixing device 20, in which a temperature detector 101b for a pressing
member is opposedly disposed on the surface of a pressing member 12, has
the same constitution as the fixing device 10 shown in FIG. 2, except
that there is disposed a cooler 21 to control the surface temperature of
the pressing member 12, based on temperature values measured by the
temperature detector 101b. The cooler 21 is constituted of plural fans
(21a) and a duct for introducing Mr supplied by the fans (21a) in the
prescribed direction. An excessive increase of the temperature of the
pressing member 12 is inhibited by providing the cooler 21.

[0152] In the fixing device 20, the nip length of a fixing nip section (N)
is 20 mm.

[0153]FIG. 4 also illustrates a sectional view showing another example of
the constitution of the fixing device used in the image forming method. A
fixing device 30 is constituted of a heating roller 11, an endless belt
12A entrained about belt-entraining rollers 12a, 12b and 12g and a
compression member 12e constituting a pressure-applying member 12B, in
which a fixing nip section N is formed by the compressed portion between
a heating roller 11 and a pressure-applying member 12e constituting a
pressure-applying member 12B. The upper surface of the compression member
12e constituting the pressure-applying member 12B is covered with a
sliding sheet 12f with an embossed uneven surface. Covering the
compression member 12e with the sliding sheet 12f decreases the contact
area between the endless belt 12A and the compression member 12e,
resulting in reduced sliding resistance.

[0154] Other constitutions of the fixing device 30 are basically the same
as those of the fixing device shown in FIG. 2.

[0155] Further, in the fixing device 30, the nip length of the fixing nip
section N is 40 mm.

[0156]FIG. 5 also illustrates a sectional view showing another example of
the constitution of the fixing device used in the image forming method. A
fixing device 40 is provided with an endless belt 41A entrained about
heating rollers 41a and 41b including heating sources 45a and 45b, a
heating member 41 constituted of a pressure-applying member 41B which is
disposed in contact with the inner circumference of the endless belt 41A,
an endless belt 42A entrained about a belt-entraining roller 42a and a
pressure roller 42b, and a pressing member 42 constituted of a
pressure-applying member 42B which is disposed in contact with the inner
circumference of the endless belt 42A.

[0157] The pressure-applying member 41B is constituted of the heating
roller 41b and a pressing member 41c and has a function of pressing the
pressing member 42 from the inner circumference of the endless belt 41A
through the endless belt 41A. The pressure-applying member 42B is
constituted of a pressing roller 42b and a pressing member 42c and has a
function of pressing a heating member 41 through the endless belt 42A
from the inner circumference of the endless belt 42A. These
pressure-applying member 41B and pressure-applying member 42B apply
pressure to each other to form a fixing nip section N.

[0158] The nip length of the fixing nip section N is 55 mm in the fixing
device 40.

[0159]FIG. 6 also illustrates a sectional view showing another example of
the constitution of the fixing device used in the image forming method. A
fixing device 50 is provided, on the external surface of an external
roller 11, with an external heating roller 53 which heats the external
surface of the external roller 11 at a prescribed timing. In the drawing,
the numeral 54 designates a heating source to heat an endless belt 12A
enclosed within a belt-entraining roller.

[0160] A pressure-applying member 12B which pressurizes the heating roller
11 through the endless belt 12A is disposed on the inner circumference of
the endless belt 12A, while being in contact therewith. The
pressure-applying member 12B is constituted of a pressure roller 12c and
a pressing member 55.

[0161] In the pressing member 55, an elastomer layer 55d layered on a
supporting plate 55c formed of a metal such as stainless steel is
disposed through a shim 55b composed of a synthetic resin such as
polyphenylene sulfide (PPS) on the surface of a base plate 55a formed of
a metal such as stainless steel. Further, the entire circumference
surface of the pressing member 55 is covered with a pad sheet 55e as a
sheet-like member. The numeral 55g designates a fixing thread to fix the
supporting plate 55c onto the base plate 55a.

[0162] The inner circumference surface of the endless belt 12A is
constituted so that, for example, an amine-modified silicone oil is
coated by a lubricant-coating member 55f formed of a felt or the like,
whereby friction between the endless belt 12A and the pad sheet 55e is
reduced.

[0163] The pressing member 55 is disposed with being compressed toward the
heating roller 11 under a compressive force of 50 kgf by a compressed
coil spring (not shown in the drawing) disposed on the side of the base
plate 55a. The pressing member 55 is provided with an elastic layer 55d,
whereby the contact surface of the pad sheet 55e with the endless belt
12A is matches the outer circumference surface. Namely, when compressing
the pressing member 55 toward the heating roller 11 by a prescribed load
or more, the elastomer layer is deformed and the contact surface of the
pad sheet 55e is deformed, while being compressed along the outer
circumference surface of the heating roller 11. Accordingly, when the
pressing member 55 is compressed against the heating roller 12 by the
compressed coil spring (not shown in the drawing), the endless belt 12A
is compressively brought into contact with the heating roller 11.

[0164] Other constitutions of the fixing device 50 are basically the same
as those of the fixing device 10 shown hi FIG. 2.

[0165] Further, in the fixing device 50, the nip length of the fixing nip
section N is 19 mm.

[0166] In the present invention, in cases when employing a fixing device
of a belt-nip system, the use of a specific toner inhibits occurrence of
image slippage, while maintaining enhanced glossiness of the formed
image.

EXAMPLES

[0167] The present invention will be further described with reference to
examples but the present invention is by no means limited to these. In
Examples, unless otherwise noted, the expression, "part(s)" represents
parts(s) by mass.

[0168] The volume-based median diameter of particles dispersed in a resin
particle dispersion or a colorant particle dispersion can be measured in
accordance with the following manner and conditions.

Measurement Method:

[0169] Into a 50 ml measuring cylinder were added a few drops of a
particle dispersion for measurement and further thereto, 25 ml of pure
water was added and dispersed over 3 minutes by using an ultrasonic
washing machine (US-1, made by AS ONE co.) to prepare a measurement
sample. Then, 3 ml of the measurement sample was placed into a cell of
Microtrack UPA-150 (made by Nikkiso Corp.) and after confirming that the
value of Sample/Loading was within the range of 0.1 to 100, measurement
was conducted in accordance with the following measurement condition and
solvent condition.

[0177] The volume-based median diameter of toner particles was determined
by using a measurement apparatus in which a Coulter Multisizer 3
(produced by Beckmann Coulter Co.) was connected to a computer system
installed with software for data processing (Software V3.51).
Specifically, 0.02 g of a toner was added to 20 ml of a surfactant
solution (for example, a neutral detergent containing a surfactant
component was diluted to ten times) and fitted, and then subjected to an
ultrasonic dispersing treatment over 1 minute to prepare a toner
dispersion. The thus prepared toner dispersion was introduced by a
pipette into a beaker having ISOTON II (made by Beckman Coulter Co),
placed in a sample stand until the display density of the measurement
instrument reached 8%. Controlling the density so as to fall within this
range rendered it feasible to obtain a reproducible measurement value. In
the measurement instrument, the number of measurement particles was set
to 25000 particles and the aperture diameter was set to 50 μm, and the
measurement range of 1 to 30 μm was divided into 256 parts to
calculate frequency values and the particle diameter at a fraction of 50%
when integrated from larger particles was defined as the volume-based
median diameter.

Example 1

[0178] Step (a-1): Preparation of Resin Particle Dispersion

(1) First Polymerization:

[0179] Into a 5 liter reaction vessel fitted with a stirrer, a temperature
sensor, a condenser and a nitrogen introducing device was placed a
surfactant solution and the liquid temperature was raised to 80°
C., while stirring at a rate of 230 rpm under a nitrogen gas stream. The
surfactant solution contained 2 parts by mass of an anionic surfactant
(sodium dodecylbenzenesulfonate, which is hereinafter also denoted as
SDS) and 2900 parts by mass of deionized water. To the surfactant
solution was added 9 parts by mass of a polymerization initiator
(potassium persulfate, which is hereinafter also denoted as KPS). Further
thereto, a monomer solution comprised of 550 parts by mass of styrene,
280 parts by mass of n-butyl acrylate, 45 parts by mass of methacrylic
acid and 14.5 parts by mass of n-octyl mercaptan was dropwise added over
3 hours and after completing the addition, the reaction mixture was
maintained at 78° C. over 1 hour to prepare a dispersion (al) of
resin particles.

(2) Second Polymerization:

[0180] In 1100 parts by mass of deionized water was dissolved 12 parts by
mass of an anionic surfactant [polyoxy(2)dodecyl ether sulfuric acid
ester sodium salt] to prepare a surfactant solution. Into a monomer
composition of 245 parts by mass of styrene, 95 parts by mass of n-butyl
acrylate, 25 parts by mass of methacrylic acid and 4 parts by mass of
n-octyl mercaptan in a flask fitted with a stirrer was added 195 parts by
mass of behenyl behenate and heated at 85° C. to prepare a monomer
solution (2).

[0181] Into a surfactant solution heated to 90° C. were added 260
parts by mass of the dispersion (a1) of resin particles and the monomer
solution (2) and dispersed by mixing them in a mechanical dispersing
machine having a circulation route (CLEARMIX, made by M-Technique Co.,
Ltd.) to prepare a dispersion.

[0182] To the thus prepared dispersion was added a polymerization
initiator solution of 11 parts by mass of polymerization initiator (KPS)
dissolved in 240 parts by mass of deionized water and stirred to
85° C. over 2 hours to prepare resin particle dispersion (a2).

(3) Third Polymerization:

[0183] A monomer solution (3) composed of 450 parts by mass of styrene,
125 parts by mass of n-butyl acrylate and 8 parts by mass of n-octyl
mercaptan was prepared; a polymerization initiator solution of 10 parts
by mass of a polymerization initiator (KPS) dissolved in 200 parts by
mass of deionized water was added to the foregoing resin particle
dispersion (a2) and further thereto, the monomer solution (3) was
dropwise added under a temperature condition of 85° C. After
completing addition, stirring continued with heating over 3 hours and
then cooled to 28° C. to prepare a dispersion (A1) of resin
particles (A1) having a multi-layered structure. It was proved that the
thus prepared resin particles (A1) exhibited a volume-based median
diameter of 160 nm, a glass transition point of 40° C., a
softening point of 91° C., a storage modulus at 100° C. of
9.5×103 dyn/cm2 and a mass average molecular weight (Mw)
of 20,000. The glass transition point, softening point, storage modulus
and mass average molecular weight (Mw) were determined in the manner
described earlier.

Step (a-2): Preparation of Dispersion (C) of Shelling Resin

[0184] An aqueous surfactant solution of 2 parts by mass of an anionic
surfactant (SDS) dissolved in 2900 parts by mass of deionized water was
prepared in a reaction vessel fitted with a stirrer, a temperature
sensor, a condenser and a nitrogen introducing device. The thus prepared
aqueous surfactant solution was raised to a temperature of 80° C.,
while stirring at a rate of 230 rpm under a nitrogen stream.

[0185] After adding 9 parts by mass of a polymerization initiator (KPS) to
the aqueous surfactant solution, a monomer solution composed of 516 parts
by mass of styrene, 204 parts by mass of n-butyl acrylate, 100 parts by
mass of methacrylic acid and 22 parts by mass of n-octyl mercaptan was
added thereto over 3 hours.

[0186] After adding the foregoing monomer solution, the temperature of the
reaction mixture was maintained at 78° C. for 1 hour to prepare a
resin dispersion. To the resin dispersion after being cooled was added an
aqueous solution of 0.7 parts by mass of a surfactant (Emal E-27C, made
by KAO Co., Ltd.) dissolved in 4 parts by mass of deionized water to
prepare a dispersion (C) of resin particles (C) to form a shell layer
[hereinafter, also denoted as resin particles (C) used for shelling]. It
was proved that the thus prepared resin particles (C) used for shelling
exhibited a volume-based median diameter of 90 nm, a glass transition
point of 50° C., a softening point of 111° C., and a mass
average molecular weight (Mw) of 11,000.

Step (b): Preparation of Resin Particle Dispersion (B1)

[0187] Into a 5 liter reaction vessel fitted with a stirrer, a temperature
sensor, a condenser and a nitrogen introducing device was placed a
surfactant solution and the liquid temperature was raised to 80°
C. with stirring at a rate of 230 rpm under a nitrogen gas stream. The
surfactant solution contained 2.1 parts by mass of an anionic surfactant
(SDS) and 1550 parts by mass of deionized water. To the surfactant
solution was added 15 parts by mass of a polymerization initiator (KPS).
Further thereto, a monomer solution comprised of 195 parts by mass of
n-butyl acrylate, 60 parts by mass of itaconic acid, and 945 parts by
mass of methyl methacrylate was dropwise added over 3 hours and after
completing the addition, the reaction mixture was maintained at
78° C. for 1 hour to prepare a dispersion (B1) of resin particles.
Resin particles (B 1) exhibited a volume-based median diameter of 90 nm,
a glass transition point of 65° C., a softening point of
188° C., a storage modulus at 100° C. of 5.0×107
dyn/cm2 and a mass average molecular weight (Mw) of 300,000.

Step (c): Preparation of Colorant Particle Dispersion (X)

[0188] Into a solution of 90 parts by mass of sodium dodecyl sulfate
dissolved in 1600 parts by mass of deionized water was added 29 parts by
mass of colorant, C.I. Pigment Blue 15 (copper phthalocyanine compound),
while stirring. Then, the mixture was subjected to a dispersing treatment
by using a mechanical stirrer, CLEARMIX (made by M-Technique Co., Ltd.)
to prepare a colorant particle dispersion (X). It was proved that
colorant particles exhibited a volume-based median diameter of 110 nm.

Step (d): Coagulation/Fusion of Resin Particles (A1) and (B1)

[0189] Into a reaction vessel fitted with a stirrer, a temperature sensor,
and a condenser were added 390 parts by mass (solid content) of a resin
particle dispersion (A1), 46 parts by mass (solid content) of a resin
particle dispersion (B1), 1700 parts by mass of deionized water and 150
parts by mass of a colorant particle dispersion, while stirring. Further
thereto, an aqueous 25% by mass sodium hydroxide solution was added and
the pH was adjusted to a value of 10.0 to 10.3.

[0190] Subsequently, an aqueous solution of magnesium chloride hexahydrate
(50% by mass) was added to the foregoing dispersion over 20 minutes,
while stirring. After completing the addition, the temperature was raised
to 75 to 80° C. over 60 minutes. Under this state, the size of
coalesced particles within the reaction vessel was measured by MULTISIZER
3 (produced by Beckman Coulter Co.) When the size of coalesced particles
reached 6.5 μm,100 parts by mass of aqueous 25% by mass sodium
chloride was added to terminate growth of the particles to prepare a
dispersion of particles. Subsequently, the dispersion was heated at
78° C. with stirring over 2 hours to obtain a dispersion (1) of
aggregated particles (1) to be used for core particles of toner
particles.

Step (e): Shelling

[0191] Subsequent to formation of the core particles, 26 parts by mass
(solids) of a dispersion of the afore-described resin particles (C) used
for shelling was further added at a temperature of 75 to 83° C.
over 20 minutes. After completing the addition, stirring continued over 2
hours to allow the resin particles (c) to coagulate and fuse to form a
shell layer on the core particle.

Steps (f): Ripening

[0192] After completing the foregoing shell formation, 200 parts by mass
of an aqueous 25% by mass sodium chloride solution to terminate
coagulation and fusion of shelling particles and then, the mixture was
heated to 88° C. to perform ripening.

Steps (g) and (h): Washing and Drying

[0193] The particle dispersion formed in the step (f) was cooled at a rate
of 4° C./min, then washed with 20° C. deionized water and
dried under room temperature to prepare a toner (1) comprised of toner
particles (1).

Step (b): Preparation of Resin Particle Dispersion (B3)

[0194] Into a 5 liter reaction vessel fitted with a stirrer, a temperature
sensor, a condenser, and a nitrogen introducing device was placed a
surfactant solution and the liquid temperature was raised to 80°
C. with stirring at a rate of 230 rpm under a nitrogen gas stream. The
surfactant solution composed of 3.6 parts by mass of an anionic
surfactant (SDS) and 1550 parts by mass of deionized water. To the
surfactant solution was added 15 parts by mass of a polymerization
initiator (KPS). Further thereto, a monomer solution comprised of 195
parts by mass of n-butyl acrylate, 60 parts by mass of itaconic acid, and
945 parts by mass of methyl methacrylate was dropwise added over 3 hours
and after completing the addition, the reaction mixture was maintained at
78° C. over 1 hour to prepare a dispersion (B3) of resin particles
(B3). The thus prepared resin particles (B3) exhibited a volume-based
median diameter, a glass transition point, a softening point, a storage
modulus at 100° C. and a mass average molecular weight (Mw), as
shown in Table 1.

Example 2

[0195] A toner (2) comprised of toner particles (2) was prepared in the
same manner as in Example 1, except that the dispersion (B1) of resin
particles (B1) used in the step (d) was replaced by a dispersion (B2) of
resin particles (B2), and the amounts of the dispersion (A1), the
dispersion (B2) and deionized water were changed to 298 parts by mass
(solids), 138 parts by mass (solids) and 1695 parts by mass,
respectively.

Step (b): Preparation of Resin Particle Dispersion (B2)

[0196] Into a 5 liter reaction vessel fitted with a stirrer, a temperature
sensor, a condenser, and a nitrogen introducing device was placed a
surfactant solution and the liquid temperature was raised to 80°
C. with stirring at a rate of 230 rpm under a nitrogen gas stream. The
surfactant solution composed of 1.5 parts by mass of an anionic
surfactant, sodium dodecylsulfate (SDS) and 1550 parts by mass of
deionized water. To the surfactant solution was added 15 parts by mass of
a polymerization initiator, sodium persulfate (KPS). Further thereto, a
monomer solution comprised of 195 parts by mass of n-butyl acrylate, 60
parts by mass of itaconic acid, and 945 parts by mass of methyl
methacrylate was dropwise added over 3 hours and after completing the
addition, the reaction mixture was maintained at 78° C. over 1
hour to prepare a dispersion (B2) of resin particles (B2). The thus
prepared resin particles (B2) exhibited a volume-based median diameter, a
glass transition point, a softening point, a storage modulus at
100° C. and a mass average molecular weight (Mw), as shown in
Table 1.

Example 3

[0197] A toner (3) comprised of toner particles (3) was prepared in the
same manner as in Example 1, except that the dispersion (B1) of resin
particles (B1) used in the step (d) was replaced by a dispersion (B3) of
resin particles (B3), and the amounts of the dispersion (A1), the
dispersion (B3) and deionized water were changed to 413 parts by mass
(solids), 23 parts by mass (solids) and 1695 parts by mass, respectively.

Step (b): Preparation of Dispersion (B3) of Resin Particles (B3)

[0198] Into a 5 liter reaction vessel fitted with a stirrer, a temperature
sensor, a condenser and a nitrogen introducing device was placed a
surfactant solution and the liquid temperature was raised to 80°
C. with stirring at a rate of 230 rpm under a nitrogen gas stream. The
surfactant solution was composed of 3.6 parts by mass of an anionic
surfactant (SDS) and 1550 parts by mass of deionized water. To the
surfactant solution was added 15 parts by mass of a polymerization
initiator (KPS). Further thereto, a monomer solution comprised of 195
parts by mass of n-butyl acrylate, 60 parts by mass of itaconic acid, and
945 parts by mass of methyl methacrylate was dropwise added over 3 hours
and after completing the addition, the reaction mixture was maintained at
78° C. over 1 hour to prepare a dispersion (B3) of resin particles
(B3). The prepared resin particles (B3) exhibited a volume-based median
diameter, a glass transition point, a softening point, a storage modulus
at 100° C. and a mass average molecular weight (Mw), as shown in
Table 1.

Example 4

[0199] A toner (4) comprised of toner particles (4) was prepared in the
same manner as in Example 1, except that the ripening time in step (e)
was varied to 5.5 hours.

Example 5

[0200] A toner (5) comprised of toner particles (5) was prepared in the
same manner as in Example 1, except that the ripening time in step (e)
was varied to 1 hours.

Example 6

[0201] A toner (6) comprised of toner particles (6) was prepared in the
same manner as in Example 1, except that the dispersion (B1) of resin
particles (B1) was replaced by a dispersion (B4) of resin particles (B4),
as described below.

Step (b): Preparation of Dispersion (B4) of Resin Particles (B4)

[0202] Into a 5 liter reaction vessel fitted with a stirrer, a temperature
sensor, a condenser and a nitrogen introducing device was placed a
surfactant solution and the liquid temperature was raised to 80°
C. with stirring at a rate of 230 rpm under a nitrogen gas stream. The
surfactant solution composed of 3.6 parts by mass of an anionic
surfactant (SDS) and 1550 parts by mass of deionized water. To the
surfactant solution was added 15 parts by mass of a polymerization
initiator (KPS). Further thereto, a monomer solution comprised of 168
parts by mass of n-butyl acrylate, 60 parts by mass of itaconic acid, and
972 parts by mass of methyl methacrylate was dropwise added over 3 hours
and after completing the addition, the reaction mixture was maintained at
78° C. over 1 hour to prepare a dispersion (B4) of resin particles
(B3). The prepared resin particles (B4) exhibited a volume-based median
diameter, a glass transition point, a softening point, a storage modulus
at 100° C. and a mass average molecular weight (Mw), as shown in
Table 1.

Example 7

[0203] A toner (7) comprised of toner particles (7) was prepared in the
same manner as in Example 1, except that the dispersion (A1) of resin
particles (A1) was replaced by a dispersion (A2) of resin particles (A2).
The dispersion (A2) of resin particles (A2) was prepared in the same
manner as the dispersion (A1) of resin particles (A1) which was prepared
in the step (a-1), except that, in the second polymerization stage, the
amount of n-octyl mercaptan was change from 4 parts by mass to 3.87
parts.

Comparative Example 1

[0204] Comparative toner (8) comprised of comparative toner particles (8)
was prepared in the same manner as in Example 1, except that the ripening
time in the step (e) was varied to 8 hours.

Comparative Example 2

[0205] Comparative toner (9) comprised of comparative toner particles (9)
was prepared in the same manner as in Example 1, except that the ripening
time in the step (e) was varied to 0.5 hour.

Comparative Example 3

[0206] Into a 5 liter reaction vessel fitted with a stirrer, a temperature
sensor, a condenser, and a nitrogen introducing device was placed a
surfactant solution of 2.7 parts by mass of an anionic surfactant (SDS)
dissolved in 2800 parts by mass of deionized water and the liquid
temperature was raised to 80° C. with stirring at a rate of 230
rpm under a nitrogen gas stream. Further, the following composition was
mixed and dissolved with being heated at 78° C. to prepare a
monomer solution.

The foregoing monomer solution and the heated surfactant solution were
mixed in a mechanical dispersing machine provided with a circulation pass
to prepare emulsified particles having a uniform particle size. Further
thereto was added an aqueous solution of 11.0 parts by mass of a
polymerization initiator (KPS) dissolved in 400 parts by mass of
deionized water and stirred for 2 hours with being heated at 78°
C. to obtain a resin particle dispersion B5.

[0207] Comparative toner (10) comprised of comparative toner particles
(10) was prepared in the same manner as in Example 1, except that the
dispersion (A1) of resin particles (A1) and the dispersion (B1) of resin
particles (B1) used in the step (d) were replaced by the resin particle
dispersion (B5), and the ripening time in the step (e) was changed to 0.5
hour.

[0208] The thus obtained toners (1) to (7) were each mixed, in a V-shaped
mixer, with ferrite carrier particles exhibiting a volume-based median
diameter of 60 μm so that the toner content was 6% by mass, whereby
developers 1 to 7 were prepared. The thus prepared developers 1 to 7 were
each evaluated as below.

[0209] Further, using an atomic force microscope (AFM) SPI 3800N (produced
Seiko Instrument Co.), toner particles (1) to (7) were each observed at
room temperature with respect to a section of a particle, while being
scanned in a micro-viscoelastic mode, and it was proved that each of
binder resins had a domain/matrix structure. Further, there are shown, in
Table 2, the ratio of domains exhibiting a major axis (L) falling within
the range of 60 to 500 nm, the proportion of domains exhibiting a minor
axis (W) falling within the range of 45 to 100 nm, the arithmetic average
value of ratio (L/W) and the arithmetic average value of area S in an AMF
elastic image of a 2 μm square area and obtained by using the atomic
force microscope (AFM). The major axis (L), the minor axis (W), the
arithmetic mean value of ratio L/W and the arithmetic mean value of area
S were each measured and calculated in the manner described earlier.

[0210] Using, as a A4 size transfer material, A4-sized coated paper, POD
Gloss Coat (84.9 g/m2, made by Oji Seishi Co., Ltd.), a solid image
was formed which was set at a toner quantity of 1.2 g/cm2 in
accordance with the combination of a fixing device and a toner, as shown
in Table 3. There was used an image forming apparatus in which a
commercially available hybrid machine, bizhub PRO C6501 (made by Konica
Minolta Business Technologies Inc.) was modified and fixing devices shown
in FIGS. 2-6 were each provided. Formed images were visually observed and
evaluated based on the criteria described below. Criteria A to C are
acceptable in practice.

[0211] A: Transfer materials were conveyed without causing image slippage
and no image defect such as uneven gloss was observed,

[0215] Using POD Gloss Coat (128 g/m2, made by Oji Seishi Co., Ltd.),
a solid image was formed which was set at a toner quantity of 1.2
g/cm2 in accordance with the combination of a fixing device and a
toner, as shown in Table 3. There was used an image forming apparatus in
which a commercially available hybrid machine, bizhub PRO C6501 (made by
Konica Minolta Business Technologies Inc.) was modified and fixing
devices shown in FIGS. 2-6 were each provided. The glossiness of the
formed image was measured and evaluated based on the criteria described
below:

[0216] A: Glossiness is not less than 70%, and being excellent,

[0217] B: Glossiness is not less than 60% and less than 70%, and being
superior,

[0218] C: Glossiness is less than 60%, and being poor.

A glossiness of not less than 60% was acceptable in practice. Glossiness
was measured at a measurement angle of 75° using glossimeter
GMX-203 (produced by Murakami Shikisai-Kogaku Kenkyusho), based on the
surface of a glass with a refractive index of 1.567.

[0219] Evaluation results are shown in Table 3. In Table 3 are also shown
linear velocity, nip length, nip-transit time, fixing pressure, surface
temperature of heating member and that of pressing member and their
difference. The nip-transit time is defined as d/v, where d is the length
(mm) of a fixing nip section formed between a heating member and a
pressing member in the moving direction, and v is the linear velocity
(mm/sec). The surface temperature of the heating member or the pressing
member was measured by the method described earlier.